1. Field of the Invention
The field of the present invention relates to an apparatus for enhancing computer fault tolerance and reliability.
More particularly, the field of the invention relates to an apparatus for adding hot-swap and hot-add functionality to a computer.
2. Background
From its origins in 1982 the personal computer (PC) has evolved into a multi-function machine suitable for use in either a stand alone or networked environment. The PCs configurablity as either a standalone or network device is due in part to the development of peripheral devices which can be easily added to a PC. Peripheral devices include for example: CD-ROM drive(s), hard disk(s), tape drive(s), monitor(s), printer(s), scanner(s), network interface cards (NICs) and serial component serial interface (SCSI) controllers.
Gone are the days when adding a single device to a computer required a time-consuming and technical process, to select a variety of system resources for each card by opening the computer and physically setting the jumpers and switches on the card. Now each peripheral device comes with plug and play capability which allows a new component to be added to a computer prior to power-up without having to perform any technical analysis or procedure.
Plug and Play (PnP) is an Intel standard for the design of PC peripheral device cards. PnP technology consists of hardware and software components that card, PC, and operating system manufacturers incorporate into their products. With this technology, the user is responsible for simply inserting the card into a corresponding expansion slot on the PC. Plug and Play makes the card capable of identifying itself and the resources it requires.
Implementing Plug and Play requires a basic input output system (BIOS) on the motherboard that supports Plug and Play as well as Plug and Play expansion cards. On power-up the system's software automatically sets up a suitable configuration for the card. Interrupt (IRQ) and direct memory access (DMA) settings and input/output (I/O) and memory addresses must be configured so that each device's I/O and memory functions occupy mutually-exclusive address ranges. In order to accomplish this the system must be able to detect how many memory and I/O address ranges a device requires and the size of each. This information is included in a configuration register on each peripheral device. In addition, the system must have the capability of programming a device's address decoders in order to assign its I/O and memory non-conflicting ranges.
Peripheral devices are attached to a PC via a bus. For some time now, in PCs, in addition to the standardized industry standard architecture (ISA) bus for attachment of legacy devices such as keyboard and mouse, use has also been made of high speed Peripheral Component Interconnect (PCI) buses for attachment of peripheral devices.
The PCI bus supports PnP. The PCI bus is a local bus for personal computers that provides a high-speed data path between the microprocessor/memory systems and peripheral devices. PCI is processor independent and is available for PCs, PowerPCs and other microprocessors. The architecture is sanctioned by the PCI special interest group (SIG), supported by over 100 manufacturers. Its chief designer and promoter is Intel. The number of peripheral device controllers the bus can handle is based on loads, which have inductance, capacitance and other electrical characteristics. Normally there are 10 loads per bus. PCI compliant devices must be initialized and configured. PCI provides for totally software driven initialization and configuration via a separate configuration address space.
A PCI device is an electrical device connected to a PCI bus. A peripheral device is a device which is outside of (peripheral to) a computer system, and typically is used in storing or transferring data to and from the computer. A device adapter is typically a PCI device, packaged on a printer circuit card and plugged into a card slot on a PCI bus, and is used to connect a peripheral device or devices to a computer system. Examples of adapter cards are network interface cards (NICs) which connect a computer to a computer network, and a SCSI Host Bus Adapter (HBA) which connects a computer to a small computer storage interface (SCSI) bus. Storage devices such as disks, cd-roms, and tapes and input/output (I/O) devices such as scanners and computer network interfaces are typically connected to a SCSI bus.
For standalone configurations of a PC plug and play offers sufficient functionality. Many PC's however, function as servers which are a vital component of a network providing for example: database, storage, print or other resources for the network. When a PC functions as a server, the requirement of PnP, that the computer be turned off to add a new component or repair and replace an existing component is not acceptable. In situations such as banking, airline reservations, or the stock exchange it costs a lot of time and money to bring down the network. In these networked environment a computers ability to overcome device failure is critical.
What is needed is a way to have a machine that continues to run even though a particular PCI device, such as a NIC or SCSI goes bad. What is needed is a machine that will allow the defective or outdated peripheral device to be replaced and placed back in service while the machine continues to run. What is needed is a machine in which new devices can be added and brought into service while the machine is running.